Thermoplastic elastomer compositions

ABSTRACT

A thermoplastic elastomer composition comprises a blend of a thermoplastic component with a cured elastomer component characterised in that the elastomer component prior to curing comprises a major proportion of a main elastomer and a minor proportion of a high molecular weight reactive polymer which shows a higher crosslinking efficiency in free-radical induced vulcanisation than the main elastomer. Preferably, the high molecular weight reactive polymer comprises from (3) to (15), and more preferably (4) to (10), parts by weight per one hundred parts of the total elastomer component of the composition. The use of the high molecular weight reactive polymer in the composition improves the low temperature performance of the composition and gives improvements to the processing behaviour, the resistance to stiffening at low temperatures and recovery/relaxation properties. Preferably, the high molecular weight reactive polymer is miscible with the main elastomer in the elastomer component. The thermoplastic elastomer composition may be made by mixing the thermoplastic component and an elastomer component comprising a main elastomer and a high molecular weight reactive polymer at a temperature to cause melting of the thermoplastic component to give a melt blend of the components, and subjecting the elastomer component in the melt blend to cure in the presence of at least one curative free-radical source.

The present invention relates to thermoplastic elastomeric compositionscomprising blends of cured elastomers and thermoplastics, such aspolyolefins, in which the elastomer is cured using a combination of afree-radical initiator, such as a peroxide, and an additional highmolecular weight polymer which participates more effectively inradically induced crosslinking.

Thermoplastic elastomers comprising blends of cured elastomers andthermoplastics are well-established and are described in, for instance,U.S. Pat. No. 3,037,954, U.S. Pat. No. 4,104,210 and U.S. Pat. No.4,271,049. Such compositions are produced by a process generally knownas dynamic vulcanisation in which the elastomer is crosslinked duringmelt blending with a thermoplastic; such materials are often known asthermoplastic vulcanisates⁽¹⁾. The crosslinking introduced in theelastomer during dynamic vulcanisation is important in defining theproperties obtained from the thermoplastic vulcanisate, particularly therelaxation and recovery properties. Effective crosslinking duringdynamic vulcanisation is, therefore, an important consideration.Although many combinations of elastomers and thermoplastics have beenconsidered in the prior art, those which have been commercialisedsuccessfully have been based on butyl rubber (IIR)⁽²⁾,ethylene-propylene-diene rubber (EPDM)⁽³⁾, natural rubber (NR)⁽⁴⁾,nitrile rubber (NBR)⁽⁵⁾ or epoxidized natural rubber (ENR)⁽⁶⁾ blendedwith a polyolefin, most often polypropylene. A variety of cure systemshas been used for the key process of dynamicvulcanisation—sulphur-based, resin, peroxide (most often with a coagent)and, more recently, hydrosilane⁽⁷⁾.

Thermoplastic elastomer blends comprising blends of more than one curedelastomer and thermoplastics are also known, for instance, from U.S.Pat. No. 4,202,801. Here, the main elastomer component of thethermoplastic component, a mono olefin copolymer rubber such as EPDM,contains a significant proportion (10 to 80% by weight of the totalcomposition) of a conjugated diene rubber such as natural rubber.

The use of a coagent to increase the yield of crosslinks obtained fromperoxide curatives is commonplace and is widely reported for the purposeof dynamic vulcanisation in order to avoid the need to use excessivelyhigh levels of peroxide, as for instance in U.S. Pat. No. 4,104,210. Inincreasing the yield of crosslinks, the coagent becomes incorporated inor forms crosslinks. Crosslinking with peroxide or other reagentscapable of decomposing to give reactive free-radicals is inherently moreefficient⁽⁸⁾ in some polymers, such as those based on or containing asubstantial proportion of butadiene repeat units⁽⁹⁾, than others, suchas those based on or containing isoprene repeat units or those with lowlevels of unsaturation. Whilst liquid 1,2-polybutadiene having a lowmolecular weight (typically <5,000) is known as a coagent⁽¹⁰⁾, thepresent invention is based on the discovery of a new approach toincreasing the effectiveness of dynamic vulcanisation with peroxide orother source of free-radicals thereby imparting improvements in variousproperties of the cured composition. We have found that theseimprovements may be achieved by incorporating, into the feedstock fordynamic vulcanisation, an additional high molecular weight polymer whichshows a higher efficiency in free-radical induced vulcanisation⁽⁸⁾ thanthe main elastomer.

Accordingly, in a first aspect, the present invention provides athermoplastic elastomer composition comprising a blend of athermoplastic component with a cured elastomer component characterisedin that the elastomer component prior to curing comprises a majorproportion of a main elastomer and a minor proportion of a highmolecular weight reactive polymer which shows a higher efficiency infree-radical induced vulcanisation than the main elastomer.

In a second aspect, the present invention provides a method of making athermoplastic elastomer composition comprising the steps of mixing athermoplastic component and an elastomer component comprising a mainelastomer and a high molecular weight reactive polymer which shows ahigher efficiency in free-radical induced vulcanisation than the mainelastomer at a temperature to cause melting of the thermoplasticcomponent to give a melt blend of the components and subjecting theelastomer component in the melt blend to cure in the presence of atleast one curative free-radical source.

According to a third aspect, the present invention provides a feedstockcomposition for use in a dynamic vulcanisation process comprising amixture of a thermoplastic component and an elastomer component, theelastomer component comprising a major proportion of a main elastomerand a minor proportion of a high molecular weight reactive polymer whichshows a higher efficiency in free-radical induced vulcanisation than themain elastomer.

Advantages that may be achieved by the use of the high molecular weightreactive polymers, according to the invention, include improved lowtemperature performance, improved processing behaviour, improvedresistance to stiffening at low temperatures and improvedrecovery/relaxation properties.

The thermoplastic elastomer composition comprises a thermoplasticcomponent. Typically, this may be a polyolefin resin although otherthermoplastic polymers, such as polyamides, may also be used in theinvention. Suitable thermoplastic polyolefin resins are well-known inthe art and include products obtained by the polymerisation of one ormore 2 to 8C alkenes. Preferably, the polyolefin resin will bepolyethylene or polypropylene, with polypropylene being more preferred.

The elastomer component which is subjected to curing during the dynamicvulcanisation procedure comprises a major proportion of a main elastomerand a minor proportion of a high molecular weight reactive polymer whichshows a higher efficiency in free-radical induced vulcanisation than themain elastomer.

The main elastomer in the elastomer component is an essentiallynon-crystalline, rubbery homopolymer of a diolefin or a copolymer inwhich one component of the polymer chain is derived from a diolefin.Examples, which are non-limiting, include cis-1,4-polyisoprene (bothsynthetic and natural, as in the case of natural rubber), epoxidizedcis-1,4-polyisoprene and ethylene-propylene-diene rubber.

The minor proportion of the elastomer component is formed by a highmolecular weight reactive polymer which shows a higher efficiency infree-radical induced vulcanisation than the main elastomer. By the term“high molecular weight” as used herein, we mean polymers having a weightaverage molecular weight of at least 100,000 and typically having anumber average molecular weight of at least 40,000. By comparison,liquid 1,2-polybutadienes, as used in the prior art as coagents,typically have weight average molecular weights of less than 5000 andnumber average molecular weights of less than 2000. Such weight average(Mw) and number average (Mn) molecular weights are determined using thetechnique of Gel Permeation Chromatography (GPC), also known as SizeExclusion Chromatography, which is a well recognised analyticaltechnique for determining molecular weights of polymeric materials. Itwill, thus, be recognised that the high molecular weight reactivepolymer used in the present invention will typically have a molecularweight approximately equivalent to that of the main elastomer used inthe elastomer component of the invention. Examples of high molecularweight reactive polymers that can be used in the present inventioninclude, but are not limited to, polybutadienes (BR) which may containlow or high contents of 1,2-polybutadiene, 1,2-polybutadiene itself,acrylonitrile rubber (NBR) and styrene-butadiene rubber (SBR). Specificexamples of commercially-available high molecular weight reactivepolymers include Buna Vi70 (Bayer AG) which is an atactic high-vinylbutadiene rubber, syndiotactic 1,2-polybutadiene RB 810, RB 820 and RB830 (Japan Synthetic Rubber) and nitrile rubber with acrylonitrilecontents of 18 and 21% (Perbunan 1807 and Nipol 1094-80, respectively).

In the most preferred embodiment, the high molecular weight reactivepolymer is miscible with the main elastomer in the composition. Examplesof miscibility to give a single elastomer phase in the composition arecis-1,4-polyisoprene, including natural rubber, with 1,2-polybutadieneor polybutadiene with a substantial 1,2-content (typically at least 30%)and epoxidized cis-1,4-polyisoprene, including epoxidized naturalrubber, with acrylonitrile-butadiene rubber (nitrile rubber). It isknown that polybutadiene with a 1,2-content of 32.3% is miscible withcis-1,4-polyisoprene⁽¹¹⁾. The miscibility of polybutadiene having a1,2-content of at least 65% and natural rubber, or syntheticcis-1,4-polyisoprene, is well-established⁽¹²⁾ but unusual for such highmolecular weight polymers⁽¹³⁾. In such instances, the high molecularweight reactive polymer acting to increase the overall efficiency ofcrosslinking may be considered as not acting as a coagent in theconventional sense; the miscible blend is vulcanised as a whole, but ata higher efficiency. The miscibility of the polymers has been found toconfer additional benefits on the composition, improved low temperatureperformance for instance.

In other compositions, the high molecular weight reactive polymer isimmiscible with the main elastomer and is evident as a separate phasewithin the elastomer component of the dynamically vulcanised blend. Anexample is polybutadiene having a high 1,2-content blended withethylene-propylene-diene rubber, in which the high molecular weightreactive polymer can be readily identified by electron microscopy as aseparate phase within the ethylene-propylene-diene rubber, with a sizetypically of the order of 100 nm or less. The results we have obtainedusing a high molecular weight reactive polymer which is immiscible withthe main elastomer are surprisingly good in view of expectations basedon the prior art.

Whether the high molecular weight reactive polymer is miscible with themain elastomer or not, it can be used as part replacement of the mainelastomer in the composition.

The benefits of using a combination of free-radical source, such asperoxide, and a high molecular weight reactive polymer, rather than aconventional coagent, are ease of use—the high molecular weight reactivepolymer may be added with the other polymers as granules or pellets—andlower cost, polymers such as polybutadiene and nitrile rubber cost,typically, £1.20-1.50/kg compared with, typically, £2.00-20.00/kg forconventional coagents.

The benefits of using polybutadiene having a high 1,2-content as thehigh molecular weight reactive polymer in the preparation ofcompositions based on natural rubber are ease of use, attaining a softermaterial at similar composition and crosslink density, improvedprocessing behaviour and improved resistance to stiffening at lowtemperatures. Such a high molecular weight reactive polymer may beeither atactic, as in the Buna Vi (Bayer AG) polymer used in some of theexamples or syndiotactic such as the RB 810 (Japan Synthetic Rubber)used in other examples. The syndiotactic form is partially crystalline,but both this and the atactic form are effective in this invention.

The benefits in using nitrile rubber (NBR) as the high molecular weightreactive polymer in the preparation of compositions based on epoxidizednatural rubber are ease of use, improved processing behaviour, improvedrecovery/relaxation properties and reduced brittle temperature.Selection of NBR with the appropriate acrylonitrile content to permitmiscibility with the ENR is critical if the full benefits are to beobtained, particularly reduced brittle temperature, which arises fromthe lower glass transition temperature of the miscible blend than thatof the ENR alone.

The benefits in using high molecular weight reactive polymers in thepreparation of compositions based on main elastomers with which they arenot miscible, such as ethylene-propylene-diene rubber or epoxidized with1,2-polybutadiene, are ease of use, improved processing behaviour andimproved properties, particularly recovery/relaxation.

The composition comprising the thermoplastic component and the elastomercomponent will typically be formulated, prior to dynamic vulcanisation,to contain from 15 to 75 parts by weight of the thermoplastic componentand from 85 to 25 parts by weight of the elastomer component per onehundred parts by weight of the total of the thermoplastic component andthe elastomer component. The elastomer component typically comprisesfrom 98 to 80 parts by weight of the main elastomer and from 2 to 20parts by weight of the high molecular weight reactive polymer per onehundred parts of total elastomer. Preferably, the high molecular weightreactive polymer comprises from 3 to 15 and more preferably 4 to 10parts by weight per one hundred parts of total elastomer.

Dynamic vulcanisation is carried out by a process comprising the stepsof mixing the thermoplastic component and an elastomer componentcomprising the main elastomer and the high molecular weight reactivepolymer at a temperature at which the thermoplastic component meltsunder mixing to form a melt blend of the components and then subjectingthe elastomer component in the melt blend to cure in the presence of atleast one free-radical initiator, preferably a peroxide, such asbis(tert-butylperoxyisopropyl)benzene (DIPP).

The compositions may be melt blended by batch mixing in an internalmixer, continuous mixing in a twin screw extruder (TSE) or a combinationof the two when a 2-stage process is used. The procedures used arefamiliar to those well-versed in the art and are not limited to thosegiven specifically in the examples below. In general, the mainelastomer, the high molecular weight reactive polymer and thethermoplastic resin are mixed to melt the thermoplastic and mixing iscontinued, typically, for about 10 seconds to 5 minutes, depending onthe shear rate prevailing during mixing, in order to allow meltblending. The material can be removed from the mixer at this stage andrendered into pellets, prior to remixing with the free-radical source,for dynamic vulcanisation or the free-radical source can be added to themelt blend. It is also possible to include the free-radical source atthe beginning of the mixing process. Melt blending during crosslinkingis conducted for an appropriate time to ensure that the dynamicvulcanisation process is complete, typically for about 10 seconds to 5minutes depending on the free-radical source used and the shear rate andtemperature prevailing during mixing. If desired, one or moreplasticisers may be added at this stage. Ingredients which areconventional in the compounding of thermoplastic vulcanisates may beincorporated in the blend before or after dynamic vulcanisation.Examples of such ingredients include, but are not limited to, pigments,dyes, fillers, stabilizers, antioxidants, plasticers and process aids.The identities and the proportions used of such ingredients are wellknown in the art and need not be discussed further here.

EXPERIMENTAL

Ingredients used in the Experimental work were a viscosity-stabilisedgrade of natural rubber from Standard Malaysian Rubber (SMR CV), 50 mole% epoxidized natural rubber (Epoxyprene 50), ethylene-propylene-dienerubber (Polysar 5875 and Buna EP T 4969), high-vinyl butadiene rubber(Buna Vi70), syndiotactic 1,2-polybutadiene (JSR RB 810), nitrile rubberwith acrylonitrile contents of 18 and 21% (Perbunan 1807 and Nipol1094-80), styrene-butadiene rubber with a styrene content of 23.5%(Intol 1502), homopolymer grade polypropylene with a melt flow index of3 g/10 min (Mosten 58412), carboxylated polypropylene (PB3150)bis(tert-butylperoxyisopropyl)benzene (DIPP),2,5-bis(tert-butylperoxy)-2,5-dimethylhexane (DHBP),2,5-bis(tert-butylperoxy)-2,5-dimethyl-3-hexyne (DYBP), liquid1,2-polybutadiene (Lithene AH), m-phenylene bismaleimide (HVA-2),naphthenic oil with low viscosity (Strukthene 380), paraffinic oil withmedium viscosity (Strukpar 2280), C9-11 alkyl phthalate (911P) andIrganox 1010, Flectol H and Arbastab Z antioxidants. In the Examples,all amounts are parts by weight per hundred parts by weight of totalpolymer (pphp) unless stated otherwise.

Molecular Weight Determination

These data were obtained using the technique of Gel PermeationChromatography (GPC), otherwise known as Size Exclusion Chromatography,which is a well recognised analytical technique for determiningmolecular weights of polymeric materials. The calculation of molecularweights from experimentally determined data relies on the use ofparameters (K and α values) which are dependent upon the polymer typeand solvent used to dissolve the polymer. For a given solvent, theseparameters do not vary much between polymers which are similar incomposition and for all of the 1,2-polybutadienes samples analysed here,the same values of K and a have been used.

Values of the number average molecular weight (Mn) and the weightaverage molecular weight (Mw) are given in Table 1, both types ofmolecular weight are often referred to. The values obtained are in goodagreement with values indicated in the trade literature from SynthomerLtd. who produce the liquid 1,2-polybutadiene and from JSR who produceRB810. TABLE 1 Molecular weights of 1,2-polybutadienes Commerciallyquoted Molecular weight molecular determined weight by GPC Material MnMw Mn Mw ‘High’ molecular Buna Vi 70 HM — — 174800 313900 weight 1,2-(Bayer) polybutadiene RB 810 (JSR) 120000 57400 120800 RB 820 (JSR)120000 65300 127600 ‘Low’ molecular Lithene AH 1800 1940 3410 weight1,2- (Synthomer Ltd) polybutadiene

Examples 1 (Comparative) and 2

The miscibility of cis-1,4-polyisoprene, such as NR, with high molecularweight polybutadiene containing 1,2-polybutadiene iswell-established⁽¹²⁾, and it is recorded that such miscibility extendsto 1,2-contents as low as 30%⁽¹¹⁾. A commonly used technique forindicating miscibility in polymer blends is Differential MechanicalThermal Analysis (DMTA). This technique identifies, for a miscibleblend, a single tan 6 maximum indicating a single glass transitiontemperature positioned between the glass transition temperatures for thecomponent polymers in the blend and dependent upon the composition ofthe blend. For an immiscible blend, such a single tan δ maximum is notobserved, instead, broad, multiple glass transition temperatures areobserved close to the transitions for component polymers. Forsyndiotactic high molecular weight 1,2-polybutadiene, the crystallinenature of the polymer causes phase separation on cooling of blends withcis-1,4-polyisoprene prepared in the melt. However, this phaseseparation does not occur if the melt blend is vulcanised, whereby thehigh molecular weight reactive polymer is crosslinked with thecis-1,4-polyisopene preventing separation of the phases, as demonstratedby the single glass transition observed for a vulcanised 70:30 blend(FIG. 1).

Two compositions were formulated and subjected to dynamic vulcanisation.The compositions (pre-cure) and the properties of the thermoplasticelastomer compositions obtained after dynamic vulcanisation are shownbelow in Table 2 for these Examples 1 (comparative) and 2. TABLE 2Example 1 (comparative) 2 Main elastomer - NR,(SMR CV) 73 66Thermoplastic resin - polypropylene 27 27 High M.W. reactive polymer(Buna Vi70) — 7 M-phenylene bismaleimide (HVA-2) 2.5 — Peroxide (DIPP)0.09 0.4 Properties Hardness, Shore A 67 59 M100, MPa 4.27 2.08 Tensilestrength, MPa 8.09 4.43 Tensile strength: M100 1.89 2.13 Elongation atbreak, % 267 293 Tension set, % 12.6 10.6 Compression set: 1 day at 23°C. 20 17 1 day at 100° C. 34 30 Change in hardness, Shore A 1 day at−25° C. +6 0 6 days at −25° C. +9 +5All materials contain: Calcium carbonate 35 parts; naphthenic oil 56parts; antidegradants 1.5 parts.

Table 2 presents compositions and properties of thermoplasticvulcanisates (TPVs) prepared using a conventional peroxide/coagent curesystem for dynamic vulcanisation (Example 1—comparative) with thoseaccording to the invention, i.e. without the coagent and with part ofthe NR replaced with the high molecular weight reactive polymer (Example2). The TPVs were prepared by mixing in a twin screw extruder (TSE) in 2stages. In the first stage, the main elastomer, the high molecularweight reactive polymer, thermoplastic and filler were blended and, inthe second stage, this preblend was mixed with the peroxide and otheringredients.

At a given rubber/thermoplastic ratio, compositions of Example 2 have alower hardness and modulus and better recovery properties, asdemonstrated by lower compression and tension set. Tensile strength isat least commensurate with the hardness/modulus, as indicated by thetensile strength:M100 ratio given in Table 2. Extruded tapes of theseTPVs according to Example 2 were superior in respect of surface finishin comparison with those of the comparable composition prepared with theconventional peroxide/coagent cure system of Example 1.

Examples 3-9

Table 3 presents compositions and properties of NRTPVs prepared withoutcoagent (Example 3—comparative), with liquid 1,2-polybutadiene (Example4—comparative), and with various butadiene-based polymers and copolymer(Examples 5-9). All were prepared by batch mixing the main elastomer,the high molecular weight reactive polymer or coagent, thermoplastic andfiller in an internal mixer and mixing this preblend with the peroxideand other ingredients in a TSE. TABLE 3 Example 3 4 (Comparative)(Comparative) 5 6 7 8 9 Main elastomer - NR (SMR CV) 75 75 75 75 75 7575 Thermoplastic resin- 25 25 25 25 25 25 25 polypropylene Coagent -Liq.1,2-BR, Lithene — 3.75 — — — — — AH High molecular weight — — 3.75 —— — — reactive polymer Buna Vi 70 High molecular weight — — — 3.75 — — —reactive polymer JSR RB 810 High molecular weight — — — — 3.75 — —reactive polymer High cis-BR, BR-40 High molecular weight — — — — — 3.75— reactive polymer Low cis-BR, CB55 High molecular weight reactive — — —— — — 3.75 polymer SBR, Intol 1502 Peroxide (DIPP) 0.4 0.4 0.4 0.4 0.40.4 0.4 Properties M100, MPa 3.51 3.39 3.90 3.81 3.35 3.34 3.90 Tensilestrength, MPa 7.20 6.99 8.92 7.61 5.82 8.32 7.27 Elongation at break, %326 317 317 296 286 344 269 Tension set, % 16.0 14.6 12.3 12.6 13.9 12.014.6

All materials contain: Calcium carbonate 37.5 parts; naphthenic oil 20parts; antidegradants 1.5 parts.

Tension set is lowest for Examples 5, 6 and 8 in which the highmolecular reactive polymer contains a substantial 1,2-polybutadienecontent.

One consequence of the miscible nature of blends such as Buna Vi 70 andNR is a reduction in the propensity of NR to crystallize at lowtemperatures, as demonstrated by the induction period with no increasein hardness and the lower increase in hardness recorded at −25° C. after6 days at this temperature (Table 2). This behaviour is confirmed byDifferential Scanning Calorimetry (DSC) which is a commonly usedprocedure used for measuring thermal transitions such ascrystallization. FIG. 2 indicates the degree of crystallinity of the NRcomponent of Examples 1 (comparative) and 2 after storage in a freezerat −19° C. It is seen that Example 2 exhibits an induction period of atleast 48 hr before any NR crystallinity is detected, compared withExample 1. The degree of crystallinity reached upon prolonged storage at−19° C. is also significantly lower over the same time interval forExample 2 compared with Example 1.

Polybutadiene rubber with a high cis-1,4 content, which is immisciblewith NR, is shown to be effective in enhancing crosslinking duringdynamic vulcanisation of blends in which NR is the main component by thelow tension set recorded (Example 7 in Table 3) relative to that seenfor the control material (Example 3—comparative). The tension set isalso lower than seen for where liquid 1,2-polybutadiene is used (Example4—comparative).

SBR, which is immiscible with NR, is shown to be effective in enhancingcrosslinking during dynamic vulcanisation of blends in which NR is themain component by the low tension set recorded (Example 9) in Table 3relative to that seen for the control material (Example 3—comparative).The tension set is the same as seen for where liquid 1,2-polybutadieneis used (Example 4—comparative).

Examples 10-13

The miscibility of ENR and NBR is not so widely known. As an example, itis shown here that ENR with an epoxide content of 50 mole % (ENR-50) ismiscible with NBR having a nominal acrylonitrile content of 18%(NBR-18). This is demonstrated by the observation of a single glasstransition for a 70:30 ENR-50:NBR-18 blend at −19° C. rather than twoglass transitions at temperatures close to those of ENR-50 and NBR-18(−10.5° C. and −36° C. respectively), as shown in FIG. 3. NBR having anominal acrylonitrile content of 21 mole % is not miscible with ENR-50;it is to be expected that for any given epoxide content of the ENR,there will be a particular narrow range of acrylonitrile content in NBRat which the NBR will be miscible with the ENR.

The data in FIG. 3 also demonstrates a reduction in glass transitiontemperature corresponding to some 4° C. per 10% added NBR-18 in theblend. Thus, an ENR-50 based thermoplastic vulcanizate cured usingperoxide/NBR-18 is expected to show improved low temperature propertiesdue to a reduction in glass transition temperature of the ENR-50.

That NBR-18 enhances crosslinking of ENR-50 is demonstrated in Table 4by the high cure rheometer torque and high peak cure rate for a 95:5ENR-50:NBR-18 blend (Example 11) relative to the control ENR-50 compound(Example 10—comparative) cured with 1.2 phr DHBP.

The improved recovery properties of a peroxide cured thermoplasticvulcanizate based on ENR-50 with NBR-18 (Example 13) are demonstrated inTable 5 where tension set is reduced in comparison with an ENR-50 basedthermoplastic vulcanizate cured using a liquid 1,2-polybutadiene coagent(Example 12—comparative). TABLE 4 Example 10 (Comparative) 11 Mainelastomer - ENR-50 100 95 High molecular weight reactive polymer 0 5(Perbunan 1807) Peroxide (DHBP) 1.2 1.2 Rheometer properties (180° C.)Torque rise, dNm 4.61 5.47 Peak cure rate, dNm/min 1.40 1.71

TABLE 5 Example 12 (Comparative) 13 Main elastomer - ENR-50 75 75Thermoplastic resin- 25 25 Polypropylene* Coagent - liq. 1,2-BR 3.75 —Lithene AH High molecular weight reactive polymer — 3.75 Perbunan 1807Peroxide (DIPP) 0.4 0.4 Properties M100, MPa 4.16 2.98 Tensile strength,MPa 7.67 6.46 Elongation at break, % 355 358 Tension set, % 20.0 16.0All materials contain: Calcium carbonate 37.5 parts; ester plasticizer20 parts; antidegradants 1.0 parts;*Thermoplastic resin contains carboxylated polypropylene compatibilizer.

Examples 14-17

High molecular weight 1,2-polybutadiene (RB 810), which is immisciblewith ethylene-propylene-diene rubber, is shown to be effective inenhancing crosslinking during dynamic vulcanization of a blend in whichethylene-propylene-diene rubber is the main elastomer component by thelow tension set recorded (Example 15 in Table 6) relative to that seenfor the control material (Example 14—comparative).

A further example where high molecular weight 1,2-polybutadiene (RB810), which is immiscible with ethylene-propylene-diene rubber is shownto be effective in enhancing crosslinking during dynamic vulcanisationof a blend in which ethylene-propylene-diene rubber is the mainelastomer component, is by the low tension set and low compression setrecorded (Example 17 in Table 7) relative to that seen for the controlmaterial (Example 16—comparative). Here, Examples 16—comparative andExample 17 have been mixed using a twin screw extruder in a single stageprocess. TABLE 6 Example 14 (Comparative) 15 Main elastomer - EPDM 75 75(Polysar 5875) Thermoplastic resin- 25 25 Polypropylene High molecularweight — 3.75 reactive polymer JSR RB 810 Peroxide (DIPP) 0.4 0.4Properties M100, MPa 4.33 4.56 Tensile strength, MPa 8.16 8.33Elongation at break, % 558 466 Tension set, % 23.4 19.7

All materials contain: Calcium carbonate 37.5 parts; antidegradants 1.5parts. TABLE 7 Example 16 (Comparative) 17 Main elastomer - EPDM 150 130(Buna EP T 4969) Thermoplastic resin - polypropylene 25 25 Highmolecular weight reactive polymer — 10 JSR RB 810 Peroxide (DYBP) 1.251.25 Paraffinic oil 10 20 Properties Hardness (Shore A) 63 68 M100 1.62.4 Tensile strength, MPa 3.9 4.6 Elongation at break, % 800 440 Tensionset, % 13.3 12.0 Compression set: 1 day at 23° 34 28 1 day at 70° C. 5643All compounds contain: Calcium carbonate 37.5 parts; antidegradants 1.0parts.

REFERENCES

-   (1) Chapter 7 by A. Y. Coran in “Thermoplastic Elastomers, a    Comprehensive Review”, N. R. Legge, G. Holden and H. E. Schroeder,    eds., Hanser, Munich, 1987.-   (2) TREFSIN®—Advanced Elastomer Systems-   (3) Such as SANTOPRENE®—Advanced Elastomer Systems-   (4) Such as VYRAM®—Advanced Elastomer Systems-   (5) GEOLAST®—Advanced Elastomer Systems-   (6) E²® EK Polymers-   (7) SANTOPRENE® 8000 Series, Advanced Elastomer Systems-   (8) L. D. Loan, Rubber Chem. Technology, 40 149-176, 1967.-   (9) F. W. Billmeyer, Jr., “Textbook of Polymer Science” 3^(rd) Ed.,    Wiley-Interscience, New York, 1984, pp 3-16.-   (10) J. W. Martin, Rubber Chem. Technology, 62 275-285, 1973.-   (11) S. Kawahara and S. Akiyama, Polymer Journal, 23 7-14, 1991.-   (12) S. Cook, J. Rubb. Res., 4 69-81 2001.-   (13) C. M. Roland, Rubber Chem. Technology, 62 456-497, 1989.

1. A thermoplastic elastomer composition comprising a blend of athermoplastic component with a cured elastomer component wherein theelastomer component prior to curing comprises a major proportion of amain elastomer and a minor proportion of a high molecular weightreactive polymer which shows a higher crosslinking efficiency infree-radical induced vulcanisation than the main elastomer.
 2. Acomposition according to claim 1, wherein the thermoplastic componentcomprises a polyolefin resin.
 3. A composition according to claim 2,wherein the polyolefin resin is polyethylene or polypropylene.
 4. Acomposition according to claim 3, wherein the polyolefin resin ispolypropylene resin.
 5. A composition according to claim 1, wherein theelastomer component prior to curing comprises a single elastomer phasecontaining the main elastomer and a high molecular weight reactivepolymer which is miscible with the main elastomer.
 6. A compositionaccording to claim 5, wherein the main elastomer is cis-1,4-polyisopreneand the high molecular weight reactive polymer miscible with the mainelastomer is polybutadiene having a 1,2-polybutadiene content of atleast 30%.
 7. A composition according to claim 6, wherein the mainelastomer is cis-1,4-polyisoprene and the high molecular weight reactivepolymer miscible with the main elastomer is polybutadiene having a1,2-polybutadiene content of at least 65%.
 8. A composition according toclaim 6, wherein the high molecular weight reactive polymer is1,2-polybutadiene.
 9. A composition according to claim 6, wherein themain elastomer is natural rubber.
 10. A composition according to claim5, wherein the main elastomer is epoxidized cis-1,4-polyisoprene and thehigh molecular weight reactive polymer miscible with the main elastomeris acrylonitrile-butadiene rubber having an acrylonitrile content toconfer miscibility with the main elastomer.
 11. A composition accordingto claim 10, wherein the epoxidized cis-1,4-polyisoprene is epoxidizednatural rubber.
 12. A composition according to claim 10, wherein theepoxidized cis-1,4-polyisoprene has an epoxide content of from 48 to 52mole % and the acrylonitrile-butadiene rubber has an acrylonitrilecontent of from 17 to 19%.
 13. A composition according to claim 10,wherein the epoxidized cis-1,4-polyisoprene has an epoxide content offrom 58 to 62 mole % and the acrylonitrile-butadiene rubber has anacrylonitrile content of from 20 to 23%.
 14. A composition according toclaim 1, wherein the elastomer component prior to curing comprises amain elastomer phase and a high molecular weight reactive polymer phase,the high molecular weight reactive polymer being immiscible with themain elastomer.
 15. A composition according to claim 14, wherein themain elastomer is ethylene-propylene diene rubber or epoxidized naturalrubber and the high molecular weight reactive polymer which isimmiscible with the main elastomer is polybutadiene.
 16. A compositionaccording to claim 15, wherein the polybutadiene has a high content of1,2-polybutadiene.
 17. A composition according to claim 14, wherein themain elastomer is epoxidized cis-1,4-polyisoprene and the high molecularweight reactive polymer which is immiscible with the main elastomer isacrylonitrile-butadiene rubber having an acrylonitrile content to conferimmiscibility with the main elastomer.
 18. A composition according toclaim 14, wherein the main elastomer is cis-1,4-polyisoprene and thehigh molecular weight reactive polymer which is immiscible in the mainelastomer is polybutadiene having a 1,2-polybutadiene content of lessthan 30%.
 19. A composition according to claim 14, wherein the mainelastomer is cis-1,4-polyisoprene and the high molecular weight reactivepolymer which is immiscible with the main elastomer is styrene-butadienerubber.
 20. A composition according to claim 18, wherein thecis-1,4-polyisoprene is natural rubber.
 21. A composition according toclaim 1, comprising from 15 to 75 parts by weight of the thermoplasticcomponent and 85 to 25 parts by weight of the cured elastomer componentper one hundred parts by weight of the total of the thermoplasticcomponent and the cured elastomer component.
 22. A composition accordingto claim 21, wherein the elastomer component, prior to curing, comprisesfrom 98 to 80 parts by weight of the main elastomer and from 2 to 20parts by weight of the high molecular weight reactive polymer per onehundred parts of the total elastomer.
 23. A composition according toclaim 22, wherein the elastomer component prior to curing comprises, perone hundred parts of total elastomer, from 3 to 15 parts by weight ofthe high molecular weight reactive polymer.
 24. A composition accordingto claim 23, wherein the elastomer component prior to curing comprises,per one hundred parts of total elastomer, from 4 to 10 parts by weightof the high molecular weight reactive polymer.
 25. A compositionaccording to claim 1, wherein the cured elastomer component is partiallycrosslinked.
 26. A composition according to claim 1, wherein the curedelastomer component is fully crosslinked.
 27. A method of making thethermoplastic elastomer composition of claim 1 comprising the steps ofmixing a thermoplastic component and an elastomer component comprising amain elastomer and a high molecular weight reactive polymer at atemperature to cause melting of the thermoplastic component to give amelt blend of the components and subjecting the elastomer component inthe melt blend to cure in the presence of at least one curativefree-radical source.
 28. A method according to claim 27, wherein thecurative free-radical source is a peroxide.
 29. A method according toclaim 27, wherein the curative is mixed with the thermoplastic componentand the elastomer component such that it is incorporated into the meltblend.
 30. A method according to claim 27, wherein the curative is addedto the melt blend prior to the curing stage.
 31. A feedstock compositionfor use in a dynamic vulcanisation process comprising a mixture of athermoplastic component and an elastomer component, the elastomercomponent comprising a major proportion of a main elastomer and a minorproportion of a high molecular weight reactive polymer which shows ahigher crosslinking efficiency in free-radical induced vulcanisationthan the main elastomer.
 32. A feedstock composition according to claim31, wherein the thermoplastic component comprises a polyolefin resin.33. A feedstock composition according to claim 32, wherein thepolyolefin resin is polyethylene or polypropylene resin.
 34. A feedstockcomposition according to claim 33, wherein the polyolefin resin ispolypropylene resin.
 35. A feedstock composition according claim 31,wherein the elastomer component comprises the main elastomer and a highmolecular weight reactive polymer which is miscible with the mainelastomer.
 36. A feedstock composition according to claim 35, whereinthe main elastomer is cis-1,4-polyisoprene and the high molecular weightreactive polymer miscible with the main elastomer is polybutadienehaving a 1,2-polybutadiene content of at least 30%.
 37. A feedstockcomposition according to claim 36, wherein the high molecular weightelastomer is 1,2-polybutadiene.
 38. A feedstock composition according toclaim 36, wherein the main elastomer is natural rubber.
 39. A feedstockcomposition according to claim 35, wherein the main elastomer isepoxidized cis-1,4-polyisoprene and the high molecular weight reactivepolymer miscible with the main elastomer is acrylonitrile-butadienerubber having an acrylonitrile content to confer miscibility with themain elastomer.
 40. A feedstock composition according to claim 39,wherein the epoxidized cis-1,4-polyisoprene is epoxidized naturalrubber.
 41. A feedstock composition according to claim 39, wherein theepoxidized cis-1,4-polyisoprene has an epoxide content of from 48 to 52mole % and the acrylonitrile-butadiene rubber has an acrylonitrilecontent of from 17 to 19%.
 42. A feedstock composition according toclaim 39, wherein the epoxidized cis-1,4-polyisoprene has an epoxidecontent of from 58 to 62 mole % and the acrylonitrile-butadiene rubberhas an acrylonitrile content of from 20 to 23%.
 43. A feedstockcomposition according to claim 31, wherein the elastomer componentcomprises a main elastomer and a high molecular weight reactive polymer,the high molecular weight reactive polymer being immiscible with themain elastomer.
 44. A feedstock composition according to claim 43,wherein the main elastomer is ethylene-propylene diene rubber orepoxidized natural rubber and the high molecular weight reactive polymerwhich is immiscible with the main elastomer is polybutadiene.
 45. Afeedstock composition according to claim 44, wherein the polybutadienehas a high content of 1,2-polybutadiene.
 46. A feedstock compositionaccording to claim 43, wherein the main elastomer is epoxidizedcis-1,4-polyisoprene and the high molecular weight reactive polymerwhich is immiscible with the main elastomer is acrylonitrile-butadienerubber having an acrylonitrile content to confer immiscibility with themain elastomer.
 47. A feedstock composition according to claim 43,wherein the main elastomer is cis-1,4-polyisoprene and the highmolecular weight reactive polymer which is immiscible in the mainelastomer is polybutadiene having a content of 1,2-polybutadiene lessthan 30%.
 48. A feedstock composition according to claim 47, wherein thecis-1,4-polyisoprene is natural rubber.
 49. A feedstock compositionaccording to claim 31, comprising from 15 to 75 parts by weight of thethermoplastic component and 85 to 25 parts by weight of the elastomercomponent per one hundred parts by weight of the total of thethermoplastic component and the elastomer component.
 50. A feedstockcomposition according to claim 31, wherein the elastomer componentcomprises from 98 to 80 parts by weight of the main elastomer and from 2to 20 parts by weight of the high molecular weight reactive polymer perone hundred parts of the total elastomer.
 51. A feedstock compositionaccording to claim 50, wherein the elastomer component comprises, perone hundred parts of total elastomer, from 3 to 15 parts by weight ofthe high molecular weight reactive polymer.
 52. A feedstock compositionaccording to claim 51, wherein the elastomer component comprises, perone hundred parts of total elastomer, from 4 to 10 parts by weight ofthe high molecular weight reactive polymer.
 53. A feedstock compositionaccording to claim 31 which additionally comprises at least one curativefree-radical source.
 54. A feedstock composition according to claim 53,wherein the curative free-radical source is a peroxide.
 55. A feedstockcomposition according to 31 which additionally comprises one or moreadditives selected from pigments, dyes, fillers, stabilizers,antioxidants, plasticizers and process aids.